Tertiary amines have previously been prepared by the reaction of a cyclic secondary amine with a primary alkyl halide in the presence of an acid acceptor in an organic solvent. Such reactions have the multiple disadvantages of long reaction times at high temperatures and formation of various by-products.
For instance, the alkylation of 4-(4-chlorophenyl)-piperidin-4-ol with 4-chloro-1-(4-fluorophenyl)-1-butanone requires about 40 hours at the reflux temperature of about 117.degree. C. for completion when using 4-methyl-2-pentanone as the solvent, sodium carbonate as the acid acceptor, and potassium iodide as an alkylation promoter. A modification of this procedure utilizing a 5:1 mixture of toluene and 4-methyl-2-pentanone as the reaction solvent requires 72 hours at the reflux temperature of about 110.degree. C. for completion.
During the long heating period required by this type of procedure, the reaction mixture discolors to a considerable degree presumably due to the formation of various by-products. To remove this color from the final product requires recrystallization, and often the use of decolorizing charcoal. Such procedures are both time-consuming and expensive, and result in a lower overall yield of the desired product.